This invention relates to a device for supporting the drive of a marine propulsion unit and more particularly to an improved, simplified drive shaft support for such units.
As is well known, most marine outboard drive units (either the outboard drive portion of an inboard/outboard drive or an outboard motor per se) employ a drive shaft that rotates about a vertically extending axis and which is driven by an internal combustion engine or other prime mover. A gearing arrangement (normally bevel gears) at the lower end of the drive shaft transmits drive from the drive shaft to the propulsion device such as the propeller and propeller shaft. Frequently, a forward neutral reverse transmission is incorporated in this gearing connection.
It is the general practice to provide a thrust bearing between the lower unit outer housing and the drive shaft for taking the normal thrust forces on the drive shaft. In accordance with outboard drive conditions, however, it is well known that the driving thrusts tend to fluctuate quite widely in an outboard drive unit and hence the drive shaft will receive thrust loadings in both directions. These reversing thrusts can cause axial movement between the drive shaft and supporting housing and, accordingly, generate noise.
In order to avoid such noises as are generated by the fluctuating thrust forces, it has been the practice to provide a relatively large diameter coil spring that encircles the drive shaft and which acts between the drive shaft and drive shaft housing for urging the thrust faces of the thrust bearing into engagement with each other. Such an arrangement, however, has several disadvantages. First, the coil spring is relatively large in diameter and this can increase the diameter of the lower unit and, accordingly, adversely effect its flow resistance in the water. In addition, it is difficult to obtain the necessary biasing forces with such single coil springs.
As shown in copending application Ser. No. 66,818, entitled Drive Shaft Supporting Device for Marine Propulsion Engine, filed June 25, 1987 in my name, which application is assigned to the assignee of this application, there is disclosed one alternative supporting arrangement that offsets the deficiencies of the prior art discussed above. Although this construction has several advantages and does overcome the noted problems, further improvements are possible.
It is, therefore, a principal object of this invention to provide an improved device for supporting the drive of a marine propulsion unit.
It is another object of this invention to provide an improved supporting arrangement for a marine propulsion drive shaft wherein the use of coil springs is eliminated.
It is yet another object of this invention to provide a marine propulsion drive shaft supporting arrangement that can be utilized with conventional marine drives without necessitating significant changes in their basic structure.